Process for producing fine rubber powder by using waste rubber

ABSTRACT

This invention provides a process for producing fine rubber powders by using waste rubber, comprising the steps of pre-pulverizing waste rubber into particles with a size of 1-4 mm; soaking the particles in a solvent selected from one or more alcohols and/or ethers; and pulverizing the soaked rubber particles into rubber powders with a size of less than 180 μm. The process according to the invention is an ideal method in industry due to its low costs and without pollution.

FIELD OF THE INVENTION

[0001] The present invention relates to the recycle of industrialwastes, especially to a process for producing fine rubber powder byusing waste rubber.

BACKGROUND OF THE INVENTION

[0002] Vulcanized natural rubber and synthetic rubber (referred to aswaste rubber) are polymer elastic materials, which are considereddifficult to be recycled. The effective treatment and recycling of wasterubber is beneficial to protection of ecological environment and forsaving of natural resources.

[0003] One of the methods for recycling waste rubber is to make it intorubber powder, which can be mixed into raw rubber materials to replacepart of rude rubber. If fine rubber powder is used with a properproportion in the materials, the shrinkage and ductility of the rubbermaterials as well as some properties of the rubber product can beimproved. Rubber powder can be also used as an additive of buildingmaterials. In practice, the particle size of the rubber powder for theabove applications is less than 180 μm, which is referred to as a finerubber powder.

[0004] At present, the industrial process for producing the rubberpowder is a method of the ambient temperature pulverization and a methodof the freezing pulverization. The former is conducted by means ofshearing and cutting force of rollers to pulverize waste rubber. Thesize of most of resultant rubber powders is of 300 μm-600 μm, and thatof 180 μm, less than 5%. Although such rubber powder has a burrysurface, which is beneficial to its combination with other materials,the amount of the rubber powder in use has to be reduced because thelarger size of the rubber powder reduces its function in practical use.In the latter method, the rubber powder obtained by the former method istenderized at a freezing temperature before being continuously shearedand cut. Such method can produce rubber powders at a size of 250-500 μm,and those at a size of below 180 μm of around 20%. In addition, thesmooth surface of such rubber powder makes it difficult combine withother materials. Both the above-mentioned methods have the disadvantagesof high assumption of energy, a high investment, a low yield of finerubber powder and high costs of production.

SUMMARY OF THE INVENTION

[0005] The present invention provides a method for producing fine rubberpowders at ambient temperature so as to overcome the above-mentionedtechnical drawbacks in the prior art.

[0006] A process according to the present invention comprises:

[0007] a) pre-pulverizing waste rubber into particles with a size of 1-4mm;

[0008] b) soaking the particles in a solvent selected from one or morealcohols and ethers; and

[0009] c) pulverizing the soaked rubber particles into rubber powderswith a size of less than 180 μm.

[0010] With the process in the present invention, fine rubber powderswith a size of less than 180 μm can be produced at ambient temperatureat a yield of 100%.

BRIEF DESCRIPTION OF THE DRAWING

[0011]FIG. 1 is the flow chart according to the process of thisinvention.

DETAILED DESCRIPTION OF INVENTION

[0012] According to the invention, the process comprises:

[0013] a) pre-pulverizing waste rubber into particles with a size of 1-4mm;

[0014] b) soaking the particles in a solvent selected from one or morealcohols and ethers; and

[0015] c) pulverizing the soaked rubber particles into rubber powderswith a size of less than 180 μm.

[0016] Said alcohols and ethers in step b) usually refer to aliphaticalcohols and aliphatic ethers with less than 20 carbon atoms. In thisinvention, the aliphatic alcohols are preferably selected from the groupconsisting of n-butyl alcohol, i-butyl alcohol and cyclohexanol, and thealiphatic ethers are preferably selected from the group consisting ofn-butyl ether, dichloethyl ether and ethylene glycol butyl ether.

[0017] The time for soaking the rubber particles depends on a solventand the type of waste rubber used in the invention. Usually, the soaklasts from 30 seconds to 10 minutes.

[0018] In step c), a pulverizing machine with strong cutting andgrinding power is used. The soaked rubber can be easily treated to befine rubber powders in this step.

[0019] After being processed in step c), the fine rubber powders stillcomprise residual solvent, which can be vaporized in a drying step. Thevaporized solvent gas can be drawn out for cooling to liquidize at atemperature of 0-20° C. before flowing back to a soaking container forcyclic use. The drying step is also a part of this invention (step d) inthe invention). The temperature for drying the fine rubber powdersdepends on the boiling point of the used solvent, and is above theboiling point of the solvent.

[0020] In the process of this invention, the pre-pulverizing of mechanicroller is used to pulverize waste rubber into small particles. Such astep is beneficial to the permeation of the solvent into rubberparticles and shortens the time for soaking the rubber particles. Sincethe fine rubber powders produced have a burry surface, it is easy to mixwith other materials. Accordingly, 20-30% of such fine rubber powderscan be mixed with raw rubber powders for manufacturing tyres and 50-60%of the same can be mixed with raw rubber powders for producing rubbershoes, rubber pipes and rubber belts. The use of mixing the fine rubberpowders can not only guarantee the physical and mechanical property, butalso reduce the costs of rubber products. It is easy to get solventsused in the process of this invention, and there are no strictrequirements for purity of the solvents. What is more, the solvents canbe recycled in an airtight system.

[0021] With reference to the drawings, this invention will be furtherdescribed in detail.

[0022] As shown in FIG. 1, the waste rubber is pre-pulverized intoparticles of 1-4 mm by a rolling machine 1 with a strong shearing andcutting force. Those pulverized rubber particles below 180 μm areseparated by a cyclone 2 and transmitted directly to a stored tank offinished products. Those rubber particles bigger than 180 μm aretransmitted into a mixing groove 4 where they are mixed with a combinedsolvent consisting of n-butyl ether and i-butyl alcohol from a solventgroove 3. After being stirred, the rubber particles soaked with thesolvent are transmitted into a pulverizing machine 5, in which they arefurther pulverized into fine powders. Then, the fine rubber powders aretransmitted into a drying groove 6, where most of the residual solventof n-butyl ether and i-butyl alcohol is volatilized at a temperature of50-80° C. and the dry fine rubber powders below 180 μm are produced.

[0023] By means of adjusting the machine 1, the size of the finishedfine rubber powders can be controlled below 150 μm, below 120 μm andeven below 75 μm. A condenser 7 and the pulverizing machine 1 as well asthe drying groove 6 are installed inside the airtight system, thevolatile solvent is dawn into the condenser 7 under a vacuum device.Uncondensed solvent is drawn into an absorbing device 8, where it iscondensed, absorbed and introduced into the stored tank 3 for cyclinguse.

What I claim is:
 1. A process for producing fine rubber powders by usingwaste rubber comprising the following steps of: a) pre-pulverizing wasterubber into particles with a size of 1-4 mm; b) soaking the particles ina solvent selected from one or more alcohols and/or ethers; and c)pulverizing the soaked rubber particles into rubber powders with a sizeof less than 180 μm.
 2. The process according to claim 1 , wherein theprocess further comprises the following step of: d) drying thepulverized fine rubber powders.
 3. The process according to claim 1 ,wherein said alcohols are selected from aliphatic alcohols with lessthan 20 carbon atoms and said ethers are selected from aliphatic etherswith less than 20 carbon atoms.
 4. The process according to claim 3 ,wherein said aliphatic alcohols comprise n butanol, i-butanol andcyclohexanol.
 5. The process according to claim 3 , wherein saidaliphatic ethers comprise n-butyl ether, dichloethyl ether and ethyleneglycol butyl ether.
 6. The process according to claim 1 , wherein stepb) is performed for from 30 seconds to 10 minutes.